Whistling sound arises from cooperative resonance between lip vortices and vocal tract formants

Evidence

Sound is generated as a ring vortex forms, but further propagation of the vortex is nearly silent. Very slight oscillations in the air column leaving through the lips influence the formation of vortices, and create part of the sound emitted. Therein lies the potential for cooperative resonance. The oscillations are likely to form at one of the resonant modes of the vocal tract—the formants (see section 17.3). The question becomes, which of these modes will set up cooperative resonance with the easily influenced vortex formation? The pressure node at the lip opening is a velocity antinode—that is, velocity oscillations are maximal there, just what is needed to set up cooperation with vortex formation. The air velocity leaving the lips may be estimated by measuring the area of the opening at the lips, knowing the lung volume, and measuring the time to empty the lungs during a whistle. This works out to approximately 30 m/s for a fairly loud whistle; or about 65 mph. At 1000 Hz, the vortices are thus spaced about 3 cm apart (1000 vortices in 30 meters). — Eric J. Heller, Why You Hear What You Hear- An…, 1326

Categorization

• DEFINE: Defines cooperative resonance and explains that the lip is a velocity antinode where vortex formation couples to the vocal tract.
• SHARE: A friend who professionally whistles (or studies acoustics) would enjoy the 30 m/s and 3 cm vortex-spacing numbers.
• XREF: connects to: Lip oscillation sustains continuously while airflow and adduction persist — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1242